The importance of chain terminating or end-capping polycarbonates by means of certain molecular weight regulating or chain terminating compounds is well known. Polycarbonates which are not end-capped or chain terminated are insufficiently heat stable since the free phenolic end groups provide a reactive site which is detrimental to the stability of the carbonate polymer. Furthermore, the absence of a chain terminating or end-capping agent or condition during the preparation of aromatic polycarbonates results in a polymer with a molecular weight which often is so high that the polymer is too viscous to mold at reasonable temperatures.
Standard chain terminating agents employed in the preparation of aromatic polycarbonates are members of the phenol family such as phenol itself and tertiary butyl phenol. Other known chain terminating agents for polycarbonates include alkanol amines, disclosed in U.S. Pat. No. 3,085,992; imides, disclosed in U.S. Pat. No. 3,399,172; aniline and methyl aniline, disclosed in U.S. Pat. No. 3,275,601; primary and secondary amines, disclosed in U.S. Pat. No. 4,001,184; aromatic amines forming aryl carbamate terminal groups, disclosed in U.S. Pat. No. 3,028,365; ammonia, ammonium compounds, primary cycloalkyl amines, aliphatic amines, and aralkyl amines forming carbamate terminal groups, disclosed in U.S. Pat. No. 4,111,910.
Further, German Offenlegunsschrift No. 27 16 304, laid open Oct. 19, 1978, discloses the use, as chain terminators, of relatively long chain carboxylic acids or acid halides (C.sub.9 -C.sub.26) in conjunction with the usual phenolic chain terminator. Although melt viscosity is lowered, thereby permitting easier processing of the resin, a significant lowering of the heat resistance of the polymer as well as embrittlement of the resin upon aging at elevated temperatures also occur.
Furthermore, according to Schnell, Chemistry and Physics of Polycarbonates (1964) page 183, ammonium hydroxide and amines saponify polycarbonates back to the monomers, e.g., bisphenol-A. Likewise, U.S. Pat. No. 3,223,678 discloses that small amounts of amines such as monoethanolamine and morpholine break down or degrade the polycarbonates into lower molecular weight polycarbonates.
Thus, the area of chain terminators and their effects upon the properties of polycarbonates is generally not completely understood and is one where the empirical approach is generally the rule rather than the exception in determining whether a particular compound or class of compounds will function effectively as chain terminators for polycarbonates. This area is further complicated by the fact that not only must a particular compound function as a chain terminator, but this compound, when incorporated into the carbonate polymer chain as a terminal group, must not adversely affect the positive and advantageous properties and characteristics of the polycarbonate. Thus, while some compounds may be effective chain terminators they are not practical since they adversely affect some of the positive and advantageous properties of polycarbonates.
There thus exists a need for chain terminators which can be utilized in producing chain terminated polycarbonates which exhibit improved heat resistance while simultaneously retaining, to a substantial degree, substantially most of their other advantageous properties.